Fix memory leak in client/server2

context_buf was never free()d. Moreover, since we want to free it on error
paths as well, and even properly zeroize it in order to demonstrate good
memory hygiene, we need to make it and its length main()-scoped.
diff --git a/programs/ssl/ssl_server2.c b/programs/ssl/ssl_server2.c
index dbabc7a..bf209e8 100644
--- a/programs/ssl/ssl_server2.c
+++ b/programs/ssl/ssl_server2.c
@@ -1442,6 +1442,10 @@
     size_t cid_len = 0;
     size_t cid_renego_len = 0;
 #endif
+#if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION)
+    unsigned char *context_buf = NULL;
+    size_t context_buf_len;
+#endif
 
     int i;
     char *p, *q;
@@ -3505,7 +3509,6 @@
     if( opt.serialize != 0 )
     {
         size_t buf_len;
-        unsigned char *context_buf = NULL;
 
         mbedtls_printf( "  . Serializing live connection..." );
 
@@ -3525,6 +3528,7 @@
 
             goto exit;
         }
+        context_buf_len = buf_len;
 
         if( ( ret = mbedtls_ssl_context_save( &ssl, context_buf,
                                               buf_len, &buf_len ) ) != 0 )
@@ -3623,6 +3627,10 @@
             goto exit;
         }
 
+        mbedtls_free( context_buf );
+        context_buf = NULL;
+        context_buf_len = 0;
+
         mbedtls_printf( " ok\n" );
     }
 #endif /* MBEDTLS_SSL_CONTEXT_SERIALIZATION */
@@ -3715,6 +3723,12 @@
 
     mbedtls_free( buf );
 
+#if defined(MBEDTLS_SSL_CONTEXT_SERIALIZATION)
+    if( context_buf != NULL )
+        mbedtls_platform_zeroize( context_buf, context_buf_len );
+    mbedtls_free( context_buf );
+#endif
+
 #if defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
 #if defined(MBEDTLS_MEMORY_DEBUG)
     mbedtls_memory_buffer_alloc_status();